Field of the Invention
The present invention relates to a buckle for seat belts especially in motor-vehicles which comprises a buckle body and a tongue member engageable with the buckle body. More particularly, the present invention relates to an improved buckle for seat belts of the type provided with a slide button for disengaging a tongue member from the buckle body.
Description of the Prior Art
In these years, a number of traffic accidents are reported, especially in case of motor-vehicles. Recently, therefore, the use of a seat belt has been required for seat occupants in motor-vehicles in many countries under various traffic safety regulations for preventing their injury or physiological damage caused by any traffic accident. Thus, a great number of seat belt assemblies have been developed hitherto in accordance with the traffic safety regulations. Among these assemblies, buckles are most popular and are fundamentally required to have such properties that they can be fastened or unfastened easier in a simple manual operation. Buckles generally known for this purpose consist of two coupling components, i.e. a buckle body and a tongue member engageable with the buckle body simply by being inserted thereinto. Basically, such buckle body comprises mechanical parts capable of engagement with the tongue member and a protective plastic cover for the mechanical parts which is provided with a slide button for disengaging the tongue member from the buckle body.
Specifically, a conventional buckle body comprises generally a channel-shaped frame constructed by a bottom plate and a pair of side plates upstanding from the side edges of the bottom plate and provided at one end thereof with an opening for the insertion of a tongue plate, a hook plate rotatably supported above the bottom plate and having at its end close to the opening of the frame a lock pawl engageable with the tongue plate, a round release bar disposed above the hook plate both ends of which are positioned respectively in slits formed approximately in an "L"-shape in both side plates for controlling the movement of the release bar, an ejector interposed between the bottom plate and the hook plate for ejecting the tongue plate, and a casing made usually of a plastic material and provided with a slide button capable of slidably moving the release bar away from the opening of the frame along the slits whereby the hook plate is rotated to disengage the lock pawl from the tongue plate by the action of a spring means interposed between the release bar and the tail end of the hook plate, with the result that the unlocked tongue plate is pushed out of the buckle body by the ejector.
One example of the buckles of this type is disclosed in U.S. Pat. No. 4,384,391. On actual use, a buckle disclosed in this patent is operated in the following manner: When a tongue 1 is inserted into a locking means 2 corresponding to the buckle body, an ejector 26 is pushed inside against the action of a spring 27 to press the lower end (downwardly extending branches 11) of a locking element 9 corresponding to the hook plate whereby the locking element 9 is rotated counterclockwise in FIG. 2 with an edge 44 functioning as a fulcrum to engage two legs 13 (branched at the front end of the locking element 9) with a narrowed neck part 22 of the tongue 1. When the locking element 9 is rotated counterclockwise, a catching bar 29 corresponding to the release bar is moved by the action of a spring means 38 to a portion 31 of an "L"-shaped slit 30 thereby preventing any clockwise rotation of the locking element 9 while pressing the legs 13. When a trigger 39 corresponding to the slide button is actuated by manual pressing, the catching bar 29 is pushed inside and moves from the portion 31 to a boundary point between the portion 31 and a portion 32 in the slit 30 whereby the locking element 9 is rotated clockwise in FIG. 3 with the edge 44 functioning as a fulcrum to elevate the catching bar 29 up to the portion 32 in the slit 30, with the result that the legs 13 are disengaged from the neck part 32 of the tongue 1 and then the ejector 26 pushes the tongue 1 out of the locking means 2 by the action of the spring 27.
Another example of the buckles of this type is disclosed in U.S. Pat. No. 4,451,958. According to the buckle disclosed in this patent, a tongue 2 is inserted into a base 1 corresponding to the buckle body 1 on actual operation. When an ejector 4 is pushed by the insertion of the tongue 2, a rocker 8 corresponding to the hook plate is rotated with a lateral axis element 27 functioning as an axis while keeping contact of an internal face 25 of the rocker 8 with a retaining bar 7 corresponding to the release bar. When the rotation proceeds at a certain degree, the direction of force exerted by a spring 9 is changed to give the rocker 8 a counterclockwise moment in FIG. 2 with the lateral axis element 27 functioning as a fulcrum. Thus, the movement of the retaining bar 7, a latch 5 and the rocker 8 changes from the state as shown in FIG. 5 to the state as shown in FIG. 4 wherein the tongue 2 is engaged firmly. When a release push button 10 is actuated by manual pressing, the retaining bar 7 is pushed inside and moves to the vertical wing of a cutout 26 corresponding to the slit, ramps 18 of the push button 10 are inserted below the latch 5 to push it up thereby disengaging the latch 5 from the tongue 2. The retaining bar 7 is simultaneously moved to the upper portion of the cutout 26 by the latch 5. The force of the spring 9 is then transmitted to the rocker 8 and the ejector 4 to push the tongue out of the base 1 (change from the state as shown in FIG. 5 to the state as shown in FIG. 6).
Further example of the conventional buckles is disclosed in U.S. Pat. No. 4,454,634. When a tongue 1 is inserted into a locking device 2 corresponding to the buckle body, an ejector 31 is pushed inside whereby a detent 34 is pushed down along a part 37 of a guide slot 35 by a link 42 since the ejector 31 is connected to the link 42 through a lower pivot axle 46 and the link is connected to the detent 34 at one end 43 thereof. At the same time, a locking member 9 is pushed down to the final latch position by a detent bar 34. When the detent 34 is pushed down to the lowest position of the part 37 of the guide slot 35, the link 42 receives the counterclockwise (in FIG. 5) moment with the lowest pivot axle 46 being as an axis by the force of a spring 18. The detent 34 is then moved in outward direction parallelly to the tongue 1 and positioned in the part 36 of the guide slot 35 whereby the tongue 1 is locked firmly by the locking member 9. When a buckle trigger 16 is pushed manually, the detent 34 is moved inwardly along the part 36 of the guide slot 35. As the detent 34 is connected to the link 42, the latter is also moved inwardly parallelly to the former. When the detent 34 reaches the innermost end of the part 36, the detent 34 is pushed up along the part 37 of the slot 35 by the action of the spring 18 whereby the locking member 9 is disengaged from the tongue 1 and the force of the spring 18 is then transmitted to the link 42 and the ejector 31 to push the tongue 1 out of the locking device 2.
Besides these typical buckles, there are known some similar buckles but their structures and mechanisms are basically similar to the ones above described. In these conventional buckles, however, a mechanical part corresponding to the release bar (the reference numerals 29, 7 and 34 in the aforesaid patents) is circular in cross section. In case the shape of the release bar is a round bar, the release bar is brought into contact only in a line with a mechanical part corresponding to the control slit (the reference numerals 31 and 32, 26 and 35 in the aforesaid patents) and with a mechanical part corresponding to the hook plate (the reference numerals 9, 5 and 9 in the aforesaid patents). If a strong force exerting in the outward direction, i.e. in the direction of ejection, is applied to the tongue plate when it is engaged with a mechanical part corresponding to the buckle body, the release bar will be pressed strongly against the control slit and/or the hook plate, thus forming a linear dent on the surface of either or both of the release bar and the mechanical parts contacting therewith. The formation of such dent makes it difficult to move the release bar smoothly for engaging or disengaging the buckle parts and requires an unreasonably strong force for pressing the slide button for disengaging the tongue plate from the buckle body.
According to the recent JIS and MVSS regulations concerning seat belt assemblies including buckles, various requirements are established for buckles one of which relates to "buckle release force" stipulating a minimum force for buckle release so that seat occupants may rapidly unfasten their seat belt and escape from motor-vehicles on any traffic accident even in case an excessive tension load is applied to the buckle, for example, on crash or sudden braking. According to U.S. Federal Regulations MVSS 209, S.4.3(d)(1) relating to "buckle release force", enforced from Dec. 13, 1979, for example, buckles for safety belt have to release when a force of not more than 30 lbs (or 14 kg) is applied. Whereas, the conventional buckles above described tend to form a linear dent, for example, on the surface of the release bar after the use for a certain period of time and soon become unable to satisfy the requirement for "buckle release" because of increasing the force necessary for disengagement with the use time.
On the other hand, this problem may be solved if the release bar is formed from a plate having a rectangular form in cross section instead of a round bar, thereby increasing the contact area between the release bar and the control slit and/or hook plate. In case the round release bar is simply replaced with a rectangular release bar, however, it will often be tilted or rotated on reciprocally moving along the control slit having a complicate contour, thus failing to afford a smooth movement of the release bar. Hence, such unstable movement of the release bar may cause a fundamental mechanical fault in buckle mechanism.
The conventional buckles include such a type wherein the hook plate is supported at the lower end of its base on the bottom plate and is rotatable by a spring means in the direction of disengagement for buckle release. In this type, a friction force is exerted between the hook plate and the tongue plate and tends to disturb smooth rotation of the hook plate so that there is a possibility of failing to disengage the hook plate from the tongue plate when a tension is exerted to the buckle.
In the buckles disclosed in U.S. Pats. Nos. 4,451,958 and 4,454,634, for example, the ejector (the reference numerals 4 and 31, respectively) is connected to the supporter (the reference numerals 8 and 42, respectively) for holding and moving the release bar (the reference numerals 7 and 34, respectively). For saving the number of mechanical parts, however, only one spring means (the reference numerals 9 and 18, respectively) is used in these buckle bodies for dual purposes of moving both supporters and ejectors. In general, the action of a coil spring is exerted in a linear axial direction by elongation and compression of the coil spring. In case of the spring 9 and 18, however, the action of the coil spring used is exerted in a special direction (through a curved route). Thus, the spring means used in these buckles cannot withstand a great number of repeated uses and is poor in durability.
In case of buckles of the type disclosed in U.S. Pat. No. 4,384,391, the locking element 9 is always urged by a spring means toward the opening for insertion of the tongue plate when the buckle is not in action. According to such mechanism, the location of the hook plate generally becomes higher relative to the bottom plate so that the size of the buckle body, especially in the direction of height becomes naturally greater. In this case, it is quite impossible to design the buckle body in a compact size.
In a motor-vehicle, a buckle for seat belt is generally equipped in upstanding form to either side of a seat by means of a wire or to the inner side of the vehicle body by means of a short webbing while a tongue plate is mounted to the front end of a long webbing. In twilight or at night, a seat belt has to be fastened correctly with a buckle in the dark or under insufficient illumination. Thus, the buckle has to be easy for handling so that a seat occupant may feel for correct insertion of the tongue plate into the buckle. For this purpose, the opening of the buckle for insertion of the tongue plate preferably has such a structure that the tongue plate may be inserted by anyone into the opening merely by feeling. Further, the opening of the buckle, which is opened upward when the buckle is in an upright position, has such a structure that the opening may accept insertion of the tongue plate but reject intrusion of foreign matters such as coins or the like flat metal tips. When a coin is inadvertently entered in a buckle body of the conventional buckle through the opening for the tongue plate, it is no longer possible to insert the tongue plate into the buckle body containing a coin or the like foreign matter and it is usually very difficult to take out the coin migrating inside the buckle body.
Thus, the prior art buckles for seat belts have some or all of the above mentioned drawbacks and there is a great demand in the automobile industry for developing a new type buckle devoid of such drawbacks.